This study demonstrates alteration of cell surface, leading to enhanced adsorption of macromolecules (bovine serum albumin (BSA), dextran, and DNA), after the exposure of cells to unipolar pulsed low electric fields (LEF). Modification of the adsorptive properties of the cell membrane also stems from the observation of LEF-induced cell-cell aggregation. Analysis of the adsorption isotherms of BSA-fluorescein isothiocyanate (FITC) to the surface of COS 5-7 cells reveals that the stimulated adsorption can be attributed to LEF-induced increase in the capacity of both specific and nonspecific binding. The enhanced adsorption was consequently followed by increased uptake. At 20 V/cm the maximal binding and subsequent uptake of BSA-FITC attached to specific sites are 6.5- and 7.4-fold higher than in controls, respectively. The nonspecific LEF-induced binding and uptake of BSA are 34- and 5.2-fold higher than in controls. LEF-enhanced adsorption is a temperature-independent process, whereas LEF-induced uptake is a temperature-dependent one that is abolished at 4 degrees C. The stimulation of adsorption and uptake is reversible, revealing similar decay kinetics at room temperature. It is suggested that electrophoretic segregation of charged components in the outer leaflet of the cell membrane is responsible for both enhanced adsorption and stimulated uptake via changes of the membrane elastic properties that enhance budding and fission processes.

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Transfer of exogenous material into the cytosol of cells is one of the main challenges in drug delivery. We present a novel physical approach for efficient incorporation of macromolecules into living cells, based on exposing them to a train of unipolar electric field pulses, possessing much lower amplitude than used for electroporation. The exposure of cells to a low electric field (LEF) alters the cell surface, leading to enhanced adsorption of macromolecules and their subsequent uptake by stimulated endocytosis. The macromolecules are initially encapsulated in membrane vesicles and then, at a later stage, are released into the cytosol and interact with intracellular targets. The uptake of fluorescently labeled macromolecules is monitored using confocal microscopy and flow cytometry. The biological activities of the incorporated macromolecules are determined by biochemical methods.